Geophysical Constraints on the Thermal Structure and Rheology of the Nigerian Lithosphere: Implications for Continental Stability and Resource Distribution

The thermal structure and rheological properties of the Nigerian lithosphere exert fundamental controls on crustal stability, the distribution of geothermal resources, the depth of brittle-ductile transition zones relevant to seismicity, and the pressure-temperature conditions experienced by migrating hydrocarbons, yet these properties are very poorly constrained by data in Nigeria compared to other cratonic and passive margin settings globally. This research derives the first geophysically constrained three-dimensional thermal and rheological model of the Nigerian lithosphere by integrating surface heat flow measurements, seismic velocity models, and gravity-constrained crustal thickness data with established relationships between seismic velocity, temperature, and composition for the relevant mantle and crustal lithologies. A new compilation of 145 surface heat flow determinations from borehole temperature gradients and thermal conductivity measurements from across Nigeria is subjected to statistical quality filtering and corrections for palaeoclimatic and hydrogeological perturbations. The filtered heat flow data are used to constrain a steady-state thermal model of the lithosphere in which mantle contributions are separated from crustal radiogenic production using the seismic velocity-constrained crustal thickness and composition model. The derived lithospheric thermal model shows a systematic heat flow gradient from cool Proterozoic craton in the northwest (less than 55 milliwatts per square metre) to warm passive margin lithosphere in the south (over 85 milliwatts per square metre). The brittle-ductile transition depth computed from the thermal model ranges from 25 kilometres beneath the Benue Trough to over 40 kilometres beneath the Jos Plateau, with direct implications for the seismogenic depth distribution. Keywords: lithospheric thermal structure, rheology, heat flow, Nigeria, brittle-ductile transition